A gas turbine engine such as that used for powering an aircraft includes rotor blades such as those found in a compressor thereof which are suitably fixedly joined to a rotor disk for accommodating centrifugal and aerodynamic loads generated during operation. As the rotor disk rotates during operation, the blades joined thereto are centrifuged radially outwardly, with the centrifugal loads generated thereby being suitably channeled to the rotor disk at stresses below predetermined stress limits for ensuring an effective useful life of the bladed disk combination.
More specifically, the blade includes a dovetail which is retained in a complementary dovetail groove in the perimeter of the rotor disk for retaining the blade thereto during operation. The blade dovetail may either be an axial-entry type which is disposed in a complementary axially extending dovetail groove in the rotor disk, or may be a circumferential-entry type disposed in a complementary circumferentially extending groove in the perimeter of the rotor disk. In the latter case, for example, the blade dovetail has a width extending in the circumferential direction which is suitably large to provide a broad support for stabilizing the blade in the disk during operation and for obtaining acceptable stress levels therein.
The rotor blade typically also includes an integral platform disposed at the juncture of the blade airfoil and dovetail which provides a radially inner boundary for the airflow channeled over the airfoil during operation. The platform extends both axially upstream and downstream from the airfoil, as well as circumferentially from both sides of the airfoil to abut adjacent platforms of adjacent rotor blades for providing a substantially continuous radially inner flowpath surface in the circumferential direction at the roots of the several airfoils used in a blade row stage.
As the diameter of the rotor disk increases for larger engine designs relative to the number of blades used in a blade row, the resulting circumferential width of each platform also increases. The additional weight due to the larger platforms increases centrifugal loads which must be carried by the rotor disk, which, therefore, requires a larger disk to accommodate the centrifugal loads within acceptable stress limits. Accordingly, a lightweight platform is desired for this large diameter rotor disk application, but the lightweight platform must still have suitable structural strength and stiffness to suppress natural resonance vibratory response thereof during operation within acceptable stress limits.